1. Field of the Invention
This application is directed to lubricating compositions having improved demulsibility. This improvement is accomplished by incorporating therein a minor amount of a novel additive combination consisting of a metal-alkylaromatic synthetic sulfonate and an alkaline-earth metal alkyl phenate. This application in a more particular aspect is directed to hydraulic fluids incorporating a minor amount of said additive combination and thereby having improved demulsibility.
2. Description of the Prior Art
Modern lubricating oils and hydraulic oils require a number of features such as antiwear, anticorrosion, deposit resistance, and water separation ability. Zinc dithiophosphates can be used to provide good antiwear properties. Metal salts such as calcium sulfonates and calcium phenates can be used for rust/corrosion protection and for mild dispersant activity to reduce deposit formation. Stronger dispersants such as succinimides can be used to further enhance deposit-free protection.
U.S. Pat. No. 3,004,917 discloses the additive combination of metal sulfonates and metal salts broadly and U.S. Pat. No. 2,954,344 discloses a combination of hydrocarbon sulfonates and alkaline-earth metal alkyl phenates. It has been found that combinations of the above-described materials perform their expected functions but are generally emulsive and do not permit separation of contaminant water. Good water separation is needed to facilitate water removal in for example critical hydraulic field service such as machine tools where gross water contamination can adversely affect machining performance. However, the specific combination herein embodied in the specific ratios disclosed below have been found to accomplish the above functions and also unexpectedly provide good water separation.